This invention relates generally to a cooking magnetron system and, more particularly, to such a system using a full wave full bridge inverter controlled by a microprocessor.
Today commercially available domestic microwave ovens commonly employ microprocessor based electronic controls. Such controls typically include an entry keyboard, and a display device, each operatively connected to a microprocessor. The microprocessor contains memory which sequences the correct operation of the microwave oven following a command or request entered by the user via the keyboard. Typically, the electronic controls may display the time of day, cooking mode, cooking time selected, cooking time remaining, selection of special cooking algorithms, power level selected, food temperature selected, and food temperature measured. The microprocessor receives data from the keyboard, monitors door closure, and receives temperature data from a temperature probe or meat thermometer. Additionally, the microprocessor may control the power level by duty cycle switching of a power transformer as used in a 50 or 60 Hz LC power supply system. The electronic controls including the microprocessor may also function to turn on a cooling fan, cavity illumination lamp, and generate an audible warning or alarm.
Although the microprocessor based microwave oven control systems have been generally useful, the microcomputer controls commonly used for appliances have not been suitable for some types of power supplies. For example, typical microcomputer or microprocessor appliance control arrangements do not provide sufficiently fast control for controlling a high frequency switching inverter, such as disclosed in the hereinbefore referenced U.S. patent application Ser. No. 138,138 which operates at a switching frequency on the order of 20-30 KHz. Commonly used low cost appliance type controllers such as Texas Instruments TMS 2XXX series of 4 bit microcomputers or the generally similar Hitachi type HMCS 43 or HMCS44A, do not generate voltage logic pulses at a sufficiently high rate to use the microcomputer output for controlling the inverter frequency. Such controllers may take longer to fetch a single instruction and to cause the transfer of data than the maximum pulse width required if the inverter were to be directly driven. Limitations, such as timing considerations, therefore, pose significant problems for microprocessor control of some microwave arrangements.